Vegetable soybeans are not only tasty but healthful. They contain almost 40 percent protein (11 grams per 1/2 cup of cooked beans) and are high in vitamins A and B, calcium, iron, and fiber. Recent research shows that soybeans are high in essential fatty acids and low in saturated fat, and that increased consumption of soybean products may lower cholesterol levels and reduce the risk of heart disease, breast cancer, and osteoporosis.
When most people think of soybeans, they envision vast Midwestern fields of plants that will eventually become animal feed, cooking oil, tofu, and dozens of other soybean-based products. Few gardeners consider growing the beans themselves, let alone eating them fresh. While the typical home garden use of soybeans is as a cover crop, some varieties of the common soybean (Glycine max) have been bred to be eaten fresh. Edamame (ed-uh-mah-may), as the Japanese call vegetable soybeans, are grown in the same way as regular forage crop soybeans, but the pods are harvested at the green or "shell" stage. The green beans pack a high-protein punch and have a sweet, buttery flavor and nutty texture. I've grown them for years, and come summer my daughter always asks when the soybeans will be ready.
Not only are they tasty and nutritious, but edamame are fun to eat. Cook the fuzzy, 2- to 3-inch-long pods for 5 minutes in water, let them cool, then squeeze the beans out of the pods directly into your mouth, tossing the inedible pods aside. Japanese bars serve bowls of warm, salted edamame with beer. You can also use shelled beans in Asian recipes or salads. If you like the taste of beans, peanuts, or cowpeas, or if you want to inspire your kids to eat more vegetables, consider growing a row of edamame.
Any soybean can be harvested and eaten at the green stage, but it won't be as sweet and tender as a variety developed for eating fresh. Most of these varieties are from China (where the beans are called maodou), Taiwan, and Japan -- regions where the beans are wildly popular. Recently, some of these varieties have reached North America.
If you live in a cool-summer climate, you need to choose varieties carefully because edamame are sensitive to cool nights and take longer than bush beans to mature. Varieties listed as maturing in 70 to 80 days may take more than 100 days. In five-year trials by Washington State University's Cooperative Extension Office in Lewis County, 18 varieties were evaluated for earliness, quantity of pods, and number and size of beans (three beans per pod is considered excellent, while two beans is acceptable).
Some varieties never produced pods before frost, but others were clear winners. 'Lucky Lion', 'Sapporo Midori', and 'White Lion' matured early and developed the most and plumpest pods. Two American varieties, 'Butterbean' (not to be confused with this common name for lima beans) and 'Envy' also performed well, with 'Envy' maturing earlier.
As Easy as Beans
Edamame are as easy to grow as bush beans but take a little longer. In my Vermont garden, I've harvested plump pods in late August from a May planting. In the South, you can even have two crops: one planted in March for a May or June harvest, and another planted in September for a November harvest.
Plant edamame as you would bush beans. After the soil has warmed to 60° F, sow seeds 1 inch deep and 2 to 4 inches apart, in rows 2 feet apart. In poorer soil, mix the seed with a legume inoculant strain for soybeans before planting. Inoculants help the plants fix atmospheric nitrogen, making this key nutrient more available. To produce an abundant crop, mulch with a 2- to 4-inch layer of hay or straw to retain soil moisture and keep weeds at bay. In sandy or low-fertility soils, side-dress at flowering with a 10-20-20 fertilizer at a rate of 1 pound per 100-foot row.
Edamame have few pests and diseases. In the South, the bean leaf roller can hamper growth, and powdery mildew can rot the beans on the plant before harvest. However, these problems are rarely severe enough to reduce yields or require controls.
Harvesting edamame at the right time is critical. Beans reach their maximum sweetness about a month after flowering. The quality is best when beans fill 85 percent of the pod, which should be bright green, similar to snow peas in color. One 2-foot-tall plant may yield up to 30 pods. You can pick individual beans off the plants or pull the whole plant out of the ground when most of the beans are mature, and then pick the beans later.
Be careful when harvesting individual beans. The stems are brittle, and I've broken a few when trying to harvest too fast.
The traditional way to eat edamame is to boil or steam 2 cups at a time for 5 minutes. The beans should have a bright, not pale, green color after cooking. Let them cool, salt to taste, then eat. If you can't use them all at once, keep raw beans in the refrigerator for up to two weeks. To store them longer, blanch whole pods for 2 to 3 minutes and freeze them in the pod for up to six months.
Although edamame are usually served as a snack or appetizer, if you can resist popping them in your mouth they also make great additions to soups, stir-fries, and salads.
Charlie Nardozzi is a senior horticulturist at National Gardening.